1. Field of the Invention
This invention relates to novel liquid crystalline compounds and liquid crystal compositions containing the same. More particularly it relates to liquid crystalline compounds having an optically active group and a chiral liquid crystal composition containing the same.
The liquid crystalline compounds defined in the present application include not only compounds for which it is possible to observe their crystalline state by themselves, but also compounds for which it is impossible to observe their crystalline state, but nevertheless have a chemical structure similar to those of liquid crystal compounds and also have properties useful as a constituent of liquid crystal compositions.
2. Description of the Related Art
At present, TN (Twisted Nematic) mode display has been most broadly employed for liquid crystal elements, but this mode is inferior in the aspect of response rate to emissive mode display elements such as electroluminescent display, plasma display, etc. Thus, various attempts in this respect have been made, but nevertheless a possibility of improvement to a large extent does not seem to have been achieved. Thus, various attempts for obtaining a liquid crystal display device based on another principle, in place of TN mode display elements have been made. As one of such attempts, there is a display mode making use of ferroelectric liquid crystals (N.A. Clark et al: Applied Phys. lett., 36, 899 (1980)). This mode makes use of ferroelectric liquid crystal chiral smectic C phase (hereinafter abbreviated to SC* phase) or chiral smectic H phase (hereinafter abbreviated to SH*), and has the following three superior specific feature as compared with TN mode display:
The first specific feature is that the display elements have a very high response rate which amounts to 100 times those of TN mode display elements.
The second specific feature is that the elements have a memory effect so that the multiplex drive is easy in combination with the above high rate response properties.
The third specific feature is that by only by adjusting the reverse time of polarity, it is possible to easily obtain the gray scale as compared with TN type display mode, and hence the display mode has been considered to be suitable for graphic display.
However, in spite of such superior specific features thereof, satisfactory results have not yet been obtained in the aspect of response rate in the case of currently known ferroelectric liquid crystals and compositions and hence it seems that they have come to a deadlock prior to their practical use. This can be said to be due to the fact that development of compounds having a large spontaneous polarization value (Ps) has been late.